P0429R9 introduced the following using aliases in [container.adaptors.general]:

The following exposition-only alias templates may appear in deduction guides for container adaptors:

template<class Container>
  using cont-key-type =                                // exposition only
    remove_const_t<typename Container::value_type::first_type>;
template<class Container>
  using cont-mapped-type =                             // exposition only
    typename Container::value_type::second_type;

But I didn't find these two being used anywhere. Any information or am I missing something?